Energy Conversion in Humans

Our own bodies, like all living organisms, are energy conversion machines. Conservation of energy implies that the chemical energy stored in food is converted into work, thermal energy, and/or stored as chemical energy in fatty tissue. (See Figure 7.25.) The fraction going into each form depends both on how much we eat and on our level of physical activity. If we eat more than is needed to do work and stay warm, the remainder goes into body fat.

A schematic diagram of energy consumed by humans and converted to various other forms is shown. Food energy is converted into work, thermal energy, and stored fat depicted by an arrow branching out of food energy and ending at these three forms. Stored fat plus thermal energy is equal to the final other energy, labeled O E sub f, and nonconservative work is shown by W sub n c, which is negative, so the initial other energy, labeled O E sub i, plus W sub n c is equal to O E sub f .

Figure 7.25 Energy consumed by humans is converted to work, thermal energy, and stored fat. By far the largest fraction goes to thermal energy, although the fraction varies depending on the type of physical activity.

 

Source: Rice University, https://openstax.org/books/college-physics/pages/7-8-work-energy-and-power-in-humans
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